This repository includes my attempt as building a TypeScript language server plugin which would strip ?search and #fragment off relative path local file ESM module imports.

To test it, open this repository in VS Code, accept the prompt to switch to the workspace TypeScript version or if it doesn't show, press Cmd+Shift+P when in a TS/JS file and select TypeScript: Select TypeScript Version. Once done, open demo-ts/index.ts or demo-js/index.js and see that the mod.ts import works. Without this TS Server plugin, that import would fail. You can verify this by switching back to the VS Code's version of TypeScript. The plugin will not load in case a non-workspace version of TS Server is used.

Using the workspace version will not be needed once this work is packaged as a VS Code extension that would register the TS Server plugin automatically. This extension could then be placed in the recommended extensions in the workspace configuration of VS Code.

https://code.visualstudio.com/api/references/contribution-points#contributes.typescriptServerPlugins

Until that is done, the TypeScript version used by the workspace is placed in node_modules and the plugin is registered through tsconfig.json. There is some trickiness to loading it (it is really in node_modules/plugin and loads plugin.js) and I'm hoping this will go away once the VS Code extension way is used. More info on this in https://stackoverflow.com/a/66504080/2715716.

To test changes to the code, make them in plugin.js and then press Cmd+Shift+P and select TypeScript: Restart TS Server and monitor the Output pane channel TypeScript. This log will show whether the changed plugin was successfully added to TS Server (Starting... and Forking... will show) or not (Killing will show). In case the TS Server starts up fine, the Cmd+Shift+P TypeScript: Open TS Server log command can be used to view the TS Server log. In case it won't, this command might not work and the Log file: line path from the Output pane TypeScript channel needs to be manually opened, for example in the Integrated Terminal using code "${logFilePath}" substituting the path from the log line.